A foam laid process for making non-woven webs is an alternative to the liquid laid process (such as shown in U.S. Pat. No. 4,349,414) that has a number of advantages over the liquid process. One of the most important advantages of the foam laid process is that the specific gravity of fibers or additives may be anywhere within the range of 15-13. The basic manner in which the foam laid process is practiced, and the advantages associated therewith, are described in U.S. Pat. Nos. 3,716,449, 3,871,952, and 3,938,782 (the disclosures of which are incorporated by reference herein).
According to the present invention the foam laid process is used to produce non-woven webs that can have one, two, three, or more strata, in an effective manner. The method and apparatus according to the invention may be used with almost any cellulose and/or synthetic fibers.
More generally, according to the invention a composite may be formed of one, two or three layers, or any combination thereof. As an example of a three-layered product may be produced as a composite comprising: a top layer formed of synthetic fibers (for example polyester, polyamide, polypropylene, etc.), cellulose and/or binder fibers; a middle layer formed of synthetic fibers, cellulose fibers and/or ion exchange resins, particles, fillers, super absorbents, different kinds of fillers, including possibly in particle form; and a bottom layer formed of a mixture of synthetic and cellulose fibers. The layers may be distinct (i.e. the mixing or interaction between the adjacent layers is very weak), or they may be mixed (bound) together very efficiently.
More generally, according to the invention a composite may be formed of one, two or three layers, or any combination thereof. As an example of a three-layered product may be produced as a composite comprising: a top layer formed of synthetic fibers (for example polyester, polyamide, polypropylene, etc.), cellulose and/or binder fibers; a middle layer formed of synthetic fibers, cellulose fibers and/or ion exchange resins, sticky materials, different kinds of fillers, including possibly in particle form; and a bottom layer formed of a mixture of synthetic and cellulose fibers. The layers may be distinct (i.e. the mixing or interaction between the adjacent layers is very weak), or they may be mixed (bound) together very efficiently.
The method and apparatus specifically according to the invention are utilized in a larger foam-laid process and system in which a variety of the techniques are optimized. However according to one specific aspect of the present invention, a method of producing a non-woven web of cellulosic and synthetic fibrous material is provided which comprises the following steps: (a) Forming a first foam slurry of air, water, cellulose or synthetic fibers, and surfactant. (b) Forming a second foam slurry of air, water, cellulose or synthetic fibers, and surfactant. (c) Moving a first foraminous element in a (e.g. generally vertical, though orientation is usually not critical) first path. (d) Moving a second foraminous element in a (e.g. generally vertical) second path. (e) Passing the first foam slurry directly into contact with the first foraminous material moving in the first path. (f Passing the second foam slurry directly into contact with the second foraminous material moving in the second path. (g) Passing a third material, different from the first and second foam slurries, (e.g. generally upwardly) in between the first and second foam slurries so that the third material does not directly contact either of the first and second foraminous elements. And, (h) forming a fibrous web from the first and second foam slurries and third material by withdrawing foam and liquid from the slurries through the first and second foraminous elements.
Step (g) may be practiced by introducing a third material, such as sticky particles, or fillers, at a consistency of between about 5-20% that would tend to stick to the first and second foraminous elements (such as conventional forming wire belts) if allowed to contact them. Steps (a) and (b) may be practiced by introducing first and second foam slurries that are different than each other.
Steps (e) and (f) are typically practiced in a headbox and there is a further step of introducing substantially pure foam into one or both of the first and second foam slurries just before the headbox. The introduction of the substantially pure foam into the fiber foam slurry improves the flowability of the foam and has other advantages. The third material is introduced directly into contact with the first and second foam slurries, there being no necessity to provide an air gap or the like between them. The final non-woven web leaving the former produced may have a consistency of about 20-60%, with a basis weight variation of less than about one-half percent.
According to another aspect of the present invention a former, which may be a twin wire former, an inclined wire former, a rotoformer, or a fourdrinier former, assembly is provided comprising the following components: A former having a closed first end (e.g. bottom), closed first and second sides, and an interior volume. A second end (e.g. top) of the former provided by a moving at least one (e.g. first and second) foraminous element. An interior structure (e.g. substantially vertical) between (and possibly generally parallel) to the first and second sides, and having a plurality of conduits therein extending from the former first end toward the second end. The interior structure defining the interior volume into a first volume on one side thereof and a second volume on the other side thereof. Means for introducing a first fiber/foam slurry into the first volume, and a second fiber/foam slurry into the second volume. Means for withdrawing foam from the first and second slurries through the one, or first and second, foraminous elements to form a non woven web on the foraminous element or elements. And, means for introducing a third material into the conduits within the interior structure.
The means for withdrawing foam from the first and second slurries through the foraminous element(s) may comprise any conventional means for that purpose, such as suction rollers, pressing rollers, or other conventional structures. In the preferred embodiment illustrated in the drawings first and second suction box assemblies are provided mounted on the opposite sides of the interior structure from first and second foraminous elements.
The means for introducing first and second foam slurries into the first and second volumes may comprise any conventional type of conduit, nozzle, orifice, header, or the like. Typically a plurality of conduits are provided disposed on the first end (e.g. bottom) of the former and facing the second end (e.g. upwardly), and/or conduits, nozzles, orifices or the like are provided for introducing the foam slurry into the first and second side walls of the headbox. Foaming nozzles are typically connected to at least one of the conduits connected to the first end (e.g. bottom) of the former, the side walls of the former, and disposed within the conduits themselves.
While the former is described as generally vertical, with the second end the top, it may have a wide variety of other orientations, including a wide variety of inclines (e.g. about 45xc2x0 and the third material moving generally upwardly at about 45xc2x0), or the second end forming the bottom. The plurality of conduits may have a first small cross-sectional area adjacent the headbox bottom and a second cross-sectional area, at least twice as great as the first cross-sectional area, adjacent the top. For example the conduits may open into the interior volume at the top of the interior structure, and flare outwardly so that at the top the conduits extends almost completely across the top of the interior structure.
Typically the interior structure is positioned with respect to the foraminous elements so that material introduced through the interior structure will not directly contact the first and second foraminous elements. This is particularly useful for introducing sticky third materials, but may also be useful when forming stratified structures, including a foam fiber slurry as the third material. The first and second fiber foam slurries may be the same, or different, from each other and from the third material (if a foam slurry).
The method and apparatus specifically according to the invention are utilized in a larger foam-laid process and system in which a variety of the techniques are optimized. However according to one specific aspect of the present invention, a method of producing a non-woven web of cellulosic and synthetic fibrous material is provided which comprises the following steps: (a) Forming a first foam slurry of air, water, cellulose or synthetic fibers, and surfactant. (b) Forming a second foam slurry of air, water, cellulose or synthetic fibers, and surfactant. (c) Moving a first foraminous element in a first path. (d) Moving a second foraminous element in a second path, a nip area provided at a location along the first and second paths. (e) Passing the first foam slurry directly into contact with the first foraminous material moving in the first path. (f) Passing the second foam slurry directly into contact with the second foraminous material moving in the second path. (g) Passing at least a third material, different from the first and second foam slurries, in between the first and second foam slurries so that the third material does not directly contact either of the first and second foraminous elements, and by introducing the third material at a plurality of different points, e.g. spaced different distances from the nip area, and/or make stripes within the product using the third material. And, (h) forming a fibrous web from the first and second foam slurries and third material by withdrawing foam and liquid from the slurries through the first and second foraminous elements.
Step (g) may be practiced by introducing a third material that would tend to stick to the first and second foraminous elements (such as conventional forming wire belts) if allowed to contact them. Steps (a) and (b) may be practiced by introducing first and second foam slurries that are different than each other.
Steps (e) and (f) are typically practiced in a headbox and there is a further step of introducing substantially pure foam into one or both of the first and second foam slurries just before the headbox. The introduction of the substantially pure foam into the fiber foam slurry improves the flowability of the foam and has other advantages. The third material is introduced directly into contact with the first and second foam slurries, there being no necessity to provide an air gap or the like between them. The final non-woven web leaving the former may have a consistency of about 20-60%, with a basis weight variation of less than about one-half percent.
The method may be implemented wherein step (g) is further practiced by automatically adjusting the positions of at least some of the plurality of points when desired to adjust the introduction points in a first dimension toward and away from the nip area; and/or wherein step (g) is further practiced to automatically adjust at least some of the plurality of points in a second dimension substantially transverse to the first dimension. The method may also include the situation wherein step (g) is practiced utilizing a plurality of distinct conduits, the conduits being of at least two different lengths; and steps (e), (f), and (g) may be practiced by providing dividing walls extending part of the length of the conduits toward the nip area.
Step (g) is preferably further practiced by passing the third material in between the first and second foam slurries after the first and second foam slurries have contacted the first and second foraminous elements, respectively, and foam and liquid are being withdrawn therefrom, or at least at such a late stage where the third material does not have sufficient time to mix with the other materials/layers before web formation of the other materials/layers starts. Step (g) may also be practiced by passing third and fourth materials, different from each other and both different from the first and second foam slurries, in between the first and second foam slurries, the third and fourth materials being introduced at spaced different distances from the nip area, and/or in a perpendicular dimension.
According to another aspect of the present invention a wire former assembly (twin wire, inclined wire, etc.) may be provided comprising the following components: A former having a closed first end, closed first and second sides, and an interior volume. A second end of the former provided by a moving at least one (e.g. first and second) foraminous element. An interior structure between the first and second sides, the interior structure defining the interior volume into a first volume on one side thereof and a second volume on the other side thereof. Means for introducing a first fiber/foam slurry into the first volume, and a second fiber/foam slurry into the second volume. Means for withdrawing foam from the first and second slurries through the foraminous element(s) to form a non-woven web on the foraminous element(s). And, means for introducing at least a third material through the interior structure, in such a way that the third material forms stripes in the web produced.
The means for introducing the at least third material may comprise any conventional fluidic structures such as nozzles, baffles, manifolds, pumps, or the like. Preferably the introducing means comprise at least a first plurality of pipes having a first effective length, though also a second plurality of pipes having a second effective length different than the first length may be used. Also more than two sets of pipes may be used.
There also may be powered means for moving the introducing means to different positions within the interior structure to adjust the location within the interior structure that the third material is introduced. The powered moving means may comprise any conventional structures such as pneumatic or hydraulic cylinders, rack and pinion gearing, screw threaded shafts with traveling nuts, etc. The powered moving means may comprise a first moving means operatively connected to the first plurality of pipes, and a second moving means, distinct from the first moving means and operating independently therefrom, operatively connected to the second plurality of pipes. The powered means may also comprise means for moving the introducing means toward and away from the second end of the former, and may still further comprise means for moving the introducing means in a dimension substantially transverse to toward and away from the second end of the former.
Preferably the interior structure is positioned at substantially all times during the normal range of movement thereof to discharge the at least third material at a location, e.g. preferably past where the means for withdrawing foam from the first and second slurries starts withdrawing foam from the slurries, or at least at such a late stage where the third material does not have sufficient time to mix with the other materials/layers before web formation of the other materials/layers starts. The interior structure may also further comprise first and second substantially solid wall elements straddling the first and second plurality of pipes and disposed between the first and second plurality of pipes and the foraminous element(s), the wall elements having a terminal portion closest to the second end of the former at a location past where the means for withdrawing foam from the first and second slurry starts withdrawing foam from the slurries. The first and second wall elements typically do not extend as far as the first and second plurality of pipes toward the second end of the former.
The former first end may be above the former second end, and a void space may exist above the terminal portions of the wall elements in-between the wall elements; however the former may have any orientation with respect to the vertical. This void area may be slightly pressurized if desired. Alternatively, the at least third material introducing means may further comprise introduction openings at the first end of the former spaced from the terminal discharges of the first and second plurality of pipes for introducing the same material as introduced by the pipes, or a different material.
The means for withdrawing foam from the first and second slurries through the foraminous element(s) may comprise any conventional means for that purpose, such as suction rollers, pressing rollers, or other conventional structures. In the preferred embodiment illustrated in the drawings first and second suction box assemblies are provided mounted on the opposite sides of the interior structure from the foraminous element(s).
While the former is illustrated as generally vertical, with the second end the bottom, it may have a wide variety of other orientations, including a wide variety of inclines (e.g. about 45xc2x0 and the third material moving generally upwardly at about 45xc2x0), or the second end forming the top. The plurality of conduits may have a first small cross-sectional area adjacent the headbox bottom and a second cross-sectional area, at least twice as great as the first cross-sectional area, adjacent the top. For example the conduits may open into the interior volume at the bottom of the interior structure, and flare outwardly so that at the bottom the conduits extends almost completely across the top of the interior structure.
It is the primary object of the present invention to provide a method and apparatus for effectively producing a non-woven web of cellulose or synthetic fibrous material utilizing foam-laid techniques, and distinctly introduced materials. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.